As a starting material of the biosynthesis of coenzyme A, D-pantothenate is widely distributed in the plant and animal kingdoms. In contrast to humans who consume sufficient quantities of pantothenic acid via the diet, symptoms of D-pantothenate deficiency are frequently described not only for plants but also for animals. The availability of D-pantothenate is therefore of great economic interest, particularly in the animal feed industry.
Conventionally, D-pantothenate is prepared by chemical synthesis from D-pantolactone and calcium β-alaninate (Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, 1999, electronic release, chapter “Vitamins”). The preparation of D-pantolactone requires complex, classical racemate cleavage via dieastereomeric salts. The commercial product resulting from the chemical synthesis is usually the calcium salt of D-pantothenic acid, calcium D-pantothenate.
Compared with chemical synthesis, the advantage of biotechnological production processes using microorganisms is the selective (enantiomerically pure) production of the D form of pantothenic acid, which can be used for higher organisms. A complex racemate cleavage, as required in chemical synthesis, is thus not necessary.
Numerous fermentation processes for preparing D-pantothenic acid using microorganisms are known, including in EP-0 590 857, WO 96/33283, U.S. Pat. No. 6,013,492, WO 97/10340, DE 198 46 499, EP 1 001 027, EP 1 006 189, EP 1 006 192 and EP 1 006 193.
Thus EP 1 006 189 and EP 1 001 027 describe processes for preparing pantothenate in which a content of at most 1 g/l of D-pantothenic acid in the fermentation solution is achieved. Such low pantothenic acid contents in the fermentation solution, that is to say of less than 10% by weight, based on the solids content, are unsuitable, however, for economic preparation of D-pantothenic acid-containing animal feed supplements. A further disadvantage with the processes described to date is that isolating the product from the fermentation medium requires numerous complex work-up steps. An economic preparation process on the industrial scale is not known.
German Laid Open Application DE 100 16 321 describes a fermentation process for preparing a D-pantothenic acid-containing animal feed supplement. However, an important disadvantage of this process, as with the above-described fermentation processes for preparing D-pantothenic acid, is that the pantothenic acid precursor β-alanine must be supplied to the micro-organism via the fermentation medium in order to obtain economic yields of the desired product.
In addition, U.S. Pat. No. 6,013,492 and WO 96/332839 describe working up the D-pantothenic acid from the fermentation solution by filtering off insoluble constituents (for example cell material) from the culture medium, adsorbing the filtrate to activated carbon, subsequently eluting the D-pantothenic acid with an organic solvent, preferably methanol, neutralizing with calcium hydroxide and subsequently crystallizing calcium D-pantothenate. Important disadvantages are the losses of valuable product occurring during crystallization and the use of an organic solvent which can only be removed with difficulty from the product and requires a complex solvent recovery step.
EP 0 590 857 describes a fermentation process for preparing D-pantothenic acid in which culturing a microorganism requires the feeding of β-alanine. The fermentation solution is filtered to separate off the biomass, then passed through a cation exchanger and then an anion exchanger, following this neutralizing with calcium hydroxide, concentrating by evaporation, adding activated carbon, filtering once more and crystallizing with addition of methanol and calcium chloride. The resultant calcium pantothenate-containing product, in addition to D-pantothenic acid in the form of the calcium salt, also contains calcium chloride in a molar ratio of 1:1. Decreasing the calcium chloride content requires electrodialysis with subsequent spray drying. This process has the disadvantage of being neither economical or ecological because of the multiplicity of complex process steps and the use of organic solvents.